1. Field of the Invention
Embodiments of the present invention relate generally to semiconductor lithography, photonic crystals, and photoresist compositions.
2. Background Information
Photoresists used for Extreme Ultraviolet (EUV) lithography are generally an extension of systems used for UV lithography or even e-beam resists. Typically, the wavelengths considered Extreme Ultraviolet are between 10 nm and 15 nm, or 0.01 μm to 0.015 μm. The body of the resist typically consists of a polymer that is cross-linked after thermal processing (baking) so as to create a protective barrier to follow-on processing steps. In newer resists molecular ingredients called Photo Generated Acid groups, PGAs, act as the patterning agent. Under exposure to UV light the PGAs release protons that bind to nearby monomers in the cross-linked polymer. When a developer solution is applied, these newly protonated monomer groups become soluble and leave the polymer matrix. The result is a removal of the protective cross-linked polymer in areas that have been exposed to light, thus producing a positive mask for further processing of the substrate.
There are many parameters of this chemical processing that need to be controlled and optimized. As lithography moves down into the nanometer range of definition the thickness of the photoresist needs to scale as well in order to produce patterns with reasonable vertical to horizontal aspect ratios. This in turn reduces the sensitivity of the system to light exposure as there is less absorption depth. Additionally, the use of a random, cross-linked polymer as the resist material results in line roughness due to the fundamental variations of a cross-linked polymer.